META_EXISTS_TAC : (string * thm) list * term -> goalstate

SYNOPSIS: Changes existentially quantified variable to metavariable.
DESCRIPTION: Given a goal of the form A ?- ?x. t[x], the tactic X_META_EXISTS_TAC gives the new goal A ?- t[x] where x is a new metavariable. In the resulting proof, it is as if the variable has been assigned here to the later choice for this metavariable, which can be made through for example UNIFY_ACCEPT_TAC.
FAILURE CONDITIONS: Never fails.
EXAMPLE: See UNIFY_ACCEPT_TAC for an example of using metavariables.
USES: Delaying instantiations until the correct term becomes clearer.
COMMENTS: Users should probably steer clear of using metavariables if possible. Note that the metavariable instantiations apply across the whole fringe of goals, not just the current goal, and can lead to confusion.
SEE ALSO: EXISTS_TAC, META_SPEC_TAC, UNIFY_ACCEPT_TAC, X_META_EXISTS_TAC.